The present invention claims priority from Japanese Patent Application No. 9-341448 filed Dec. 11, 1997, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an aural communication system for a digital telephone set and, particularly, to a digital telephone set using a high tone quality aural communication system capable of performing a stereo aural communication.
2. Description of Related Art
First, a conventional digital telephone set will be described.
An example of the digital telephone set is disclosed in Japanese Patent Application Laid-open No. Hei 7-111547. In the disclosed digital telephone set, a transmission charge is reduced by transmitting an externally input data as well as an aural signal through a B channel. In order to realize the simultaneous transmission of the externally input data and the aural signal, the aural signal from the digital telephone set is compressed by converting it into a PCM code and further into an adaptive differential PCM (ADPCM) code and the externally input data is converted into a 8-bit serial data. The ADPCM code and the 8-bit serial data are multiplexed in a unit frame of 8 bits and transmitted to an integrated services digital network (ISDN). An 8-bit unit frame received from the ISDN is processed in a reverse manner to the above.
Further, Japanese Patent Application Laid-open No. Hei 5-252315 discloses an example of a conventional digital telephone system. In the digital telephone system disclosed in Japanese Patent Application Laid open No. Hei 5-252315, a standard telephone set is used to input/output an aural signal with respect to a computer system. When a telephone aural mode is selected in the computer system, an aural signal from a private circuit to which the standard telephone set is connected to obtain a set of aural signal samples. The aural signal samples are converted into an aural data stream having a standard data format and the aural data stream is transferred to a telephone driver operating in a digital signal processing sub system. The telephone driver converts the aural data stream into a telephone data value and transfers the latter to a telephone circuit. The telephone circuit generates a telephone voice signal corresponding to the telephone data value and the telephone voice signal is transferred to the standard telephone set through the private circuit.
These conventional arts have a problem that a tone quality of the telephone set is insufficient. Further, these are also insufficient in transmitting voice together with ambience to another.
The reasons for these are that the telephone set has been prepared for the purpose of monaural voice conversation and requires a tone quality which is not higher than the tone quality with which such monaural conversation is possible and that the telephone set has substantially no measure against a high tone quality voice communication and a stereo voice communication. The above facts are still maintained in the present situation in which the digitalization of communication circuit is being promoted and these functions are not obtained in the digital telephone set.
In the digital telephone set disclosed in the previously mentioned Japanese Patent Application Laid-open No. Hei 5-252315, the audio signal compression technique is utilized to maintain an amount of information for the data transmission.
In the computer system disclosed in the previously mentioned Japanese Patent Application Laid-open No. Hei 7-111547, the tone quality is not improved although aural signal is treated in the telephone voice mode.
An object of the present invention is to realize a stereo aural communication by improving the tone quality of aural communication through a digital telephone set.
According to a first aspect of the present invention, a digital telephone set is provided, which is featured by comprising a digital signal transmitter/receiver for transmitting/receiving a digital signal with respect to a digital telephone circuit, a protocol control portion for transmitting/receiving various control signals through the digital signal transmitter/receiver and the digital telephone circuit and converting an information contained in the digital signal received by the digital signal transmitter/receiver into a series of information by determining the kind of the information contained in the digital signal received by the digital signal transmitter/receiver correspondingly to a protocol of the digital signal, a receiving system recognizing portion for recognizing a communication system of an aural signal information when a receiving signal information obtained by a conversion performed in the protocol control. portion is the aural signal information, receiving aural signal processing means for processing the aural signal information according to the communication system recognized by the receiving system recognizing portion and aural signal output means for converting the aural signal information processed by the receiving aural signal processing means into an analog aural signal information and supplying the analog aural signal as a sound signal. The receiving aural signal processing means includes a compressed aural signal information expanding portion for expanding the aural information correspondingly to a compression system and a compression rate used in compressing the aural signal information when it is indicated by the communication system obtained by the receiving system recognizing portion that the aural signal information is compressed and a stereo separation portion for separating the aural signal information when the communication system obtained by the receiving system recognizing portion indicates that the aural signal information is a stereo format having a right aural signal and a left aural signal. The aural signal output means includes means for supplying the stereo aural signal information as the right voice and the left voice.
The construction of the digital telephone set mentioned above is intended to receive an aural signal information from a remote side. However, it is preferable for the digital telephone set to additionally have a construction for transmitting an aural signal information to a remote side. That is, the digital telephone set preferably further comprises aural signal input means for converting an analog. aural signal information into a digital aural signal information with directivity corresponding to a right ear and a left ear, a communication system setting portion for preliminarily setting the communication system to transmit the aural signal information input from the aural signal input means to the digital telephone circuit to a compression system and the stereo system, transmitting aural signal information processing means for processing the aural signal information from the aural signal input means according to the thus set compression system and the stereo system and a communication system notifying portion for incorporating the communication system information indicative of the compression system and the stereo system of the aural signal information output from the transmitting aural signal information processing means in the protocol control information. The protocol control portion preferably transmits the protocol information including the communication system information incorporated therein by the communication system notifying portion to a remote side through the digital signal transmitter/receiver and the digital telephone circuit and transmits the aural signal information output from the transmitting aural signal information processing means after a format of the aural signal information is converted into a format compatible with the protocol of the digital telephone circuit.
The present invention can be embodied with only the construction for the aural signal transmission. That is, according to a second aspect of the present invention, the digital telephone set comprises aural signal input means for converting the aural signal information into a digital aural signal information with directivity corresponding to a right ear and a left ear, a communication system setting portion for preliminarily setting the communication system for transmitting the aural signal information input from the aural signal input means to the digital telephone circuit to a compression system and the stereo system, transmitting aural signal information processing means for processing the aural signal information from the aural signal input means according to the thus set compression system and the stereo system, a communication system notifying portion for incorporating the communication system information indicative of the compression system and the stereo system of the aural signal information output from the transmitting aural signal information processing means in the protocol control information, a protocol control portion for converting the aural signal information processed by the transmitting aural signal information processing means such that the aural signal information becomes compatible to the protocol of the digital telephone circuit and transmitting/receiving various control information including the protocol information and a digital signal transmitter/receiver for transmitting the aural signal information converted by the protocol control portion to the digital telephone circuit and transmitting/receiving the various control information between the protocol control portion and the digital telephone circuit.